Imk209 fantasia


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  • When milk becomes too acidic, like when we add lemon juice or when it goes sour, the negative charge on the casein groupings becomes neutralized.
    Now instead of pushing each other apart, the casein starts to clump together. Eventually large enough clumps are formed that we can actually see the separation, and then we have curdled milk.
    the lemon juice decreases the pH of the emulsion toward the isoelectric point of the proteins, thereby reducing the electrostatic repulsion between the droplets and causing droplet aggregation.
  • The coating is typically applied electrostatically and is then cured under heat to allow it to flow and form a "skin". 
    not having the need to clean the equipment so much, cleaner environment for
    does not require a solvent to keep the binder and filler parts in a liquid suspension form
  • Imk209 fantasia

    1. 1. Electrostatic Forcesby, FaNtasi’a the forces between particles that are caused by their electric charges.
    2. 2. • Van der Waals attractive force • Electrostatic repulsive force • Electrical double layer
    3. 3. COLLOID • Colloidal particles often carry an electrical charge and therefore attract or repel each other. • The charge of both the continuous and the dispersed phase, as well as the mobility of the phases are factors affecting this interaction.
    4. 4. Why Lemon Makes Milk Curdle??
    5. 5. Electrostatic coating • Painting industry • principle :charge powder particles to similar polarity, charged particles repel each other, forming a cloud across the coating area.
    6. 6. DLVO THEORY • Boris Derjaguin • Lev Landau • Evert Verwey • Theo Overbeek
    7. 7. VT = VA + VR + VS • Where, • VT = Total interaction force • VA = van der Waals attraction • VR = electrical double layer repulsive
    8. 8. • Two types of force in a stable colloid: van der Waals' force -attractive and binds particles together electrostatic repulsion -The total interaction potential can be calculated as a function of distance, with colloid stability being attained when two forces balance each other.
    9. 9. Figure 1: Types of colloidal stabilization • There are two fundamental mechanisms that affect dispersion stability (figure 1): Steric repulsion Electrostatic or charge stabilization
    10. 10. Application of DLVO Theory • Since 1940s, the DLVO theory has been used to explain phenomena found in colloidal science, adsorption and many other fields. Due to the appearance of nanoparticles, DLVO theory becomes even more popular. Because it can be used to explain both general nanoparticles such as fullerenes particles and microorganisms.
    11. 11. ELECTROSTATIC DOUBLE LAYER: DEFINITION  A structure that appears on the surface of an object when it is placed into a liquid  Consists of two parallel layers of charge surrounding the object  The object might be a solid particle, a gas bubble, a liquid droplet, or a porous body  Important in determining the physical properties of the system as a whole
    12. 12. FIRST LAYER SECOND LAYER  The surface charge (either positive or negative)  Comprises ions adsorbed directly onto the object due to a host of chemical interactions  Is firmly adsorbed on the surface of the object  Also called the diffuse layer  Composed of free ions attracted to the surface charge via the Coulomb force  Electrically screens the first layer  Is loosely associated with the object ELECTROSTATIC DOUBLE LAYER:
    14. 14. Zeta potential • electrical potential that exists at the "shear plane" of a particle, which is some small distance from its surface. • electric potential in the interfacial double layer (DL) at the location of the slipping plane versus a point in the bulk fluid away from the interface • charge that develops at the interface between a solid surface and its liquid medium
    15. 15. • Zeta potential is considered to be the electric potential of this inner area including this conceptual sliding surface.
    16. 16. Zeta Potential (Smoluchowski’s Formula) The Smoluchowski (for high ionic strengths) or Huckel (for low ionic strengths) equations are used to obtain the Zeta potential from the measured mobilities.
    17. 17. Zeta Potential vs. Surface Potential The relationship between zeta potential and surface potential depends on the level of ions in the solution.
    18. 18. Zeta potential [mV] Stability behavior of the colloid from 0 to ±5 Rapid coagulation or flocculation from ±10 to ±30 Incipient instability from ±30 to ±40 Moderate stability from ±40 to ±60 Good stability more than ±61 Excellent stability
    20. 20. Effect of ionic strength and pH
    21. 21. Ionic stabilization… • charged groups on the surface of the emulsion droplets will increase the repulsive forces - Ionic emulsifier will form an electricity charge double layer in the aqueous solution surrounding each oil droplet.
    22. 22. • Ionic strength effect??? - the thickness of the electrical double layer • Ionic strength - electrical repulsion is greater than Van der Waals attraction Ionic stabilization…
    23. 23. • almost all food formulation will contain some proteins –proteins may be neutralpositively charged, or negatively charged depending of the pH of the system compared to their isoelectric point, pI (pH < pI, positive charge; pH > pI, net negative charge). • The charge on a droplet is important because it determines the nature of its interactions with other charged species. Two droplets charges of opposite sign = attracted toward each other two droplets charges of similar sign = repelled to each other
    24. 24. • properties of emulsions stabilized by; -ionized emulsifiers (pH and ionic strength of the aqueous phase) • pH is adjusted 1. emulsifier loses its charge, or 2. if salt is added to “screen” the electrostatic interactions between the droplets (repulsive forces may no longer be strong enough to prevent the droplets from aggregating)
    25. 25. Remember!!! -the energy barrier modified by changing the pH and pI -effect directly the forces involved • Increase pH above the isoelectric point (pI) • the electrostatic interaction energy • Decreasing ionic strength -Increase energy barrier -stabilizing the suspension -increase turbidity
    26. 26. For example from our previous slide, • The situation whereby ‘Why Lemon Makes Milk Curdle??’ • decreases the pH of the emulsion toward the isoelectric point of the proteins, • thereby reducing the electrostatic repulsion between the droplets and causing droplet aggregation.
    27. 27. Prepared by; FANTASIA